292
Diekmann et al.
1996). Apart from local kaolinite-bearing rocks and
soils, no significant continental kaolinite sources
occur between 30 0 S and the Southern Ocean.
Therefore substantial kaolinite transport to the south
can only be achieved through advection of kaolinite
within deep water masses from the north moving
south.
Main jets ofNADW flow are confined to the
continental margins of the western South Atlantic
basins where they constitute the deep western
boundary current above 4000 m water depth
(Faugeres et al. 1993) (Fig. I). On its course to
the south, NADW sweeps off the kaolinite-rich
sediments in the Vema Channel region (Jones 1984;
Masse et al. 1996). Particularly those sediments
trapped at the Sao Paulo Plateau may be entrained
in particulate suspensions of the NADW by reworking and resuspension due to bottom current
turbulence and/or bioturbation (Jones 1984). The
Sao Paulo Plateau forms a broad slope area in 2700
to 3300 m water depth, which builds up the western flank of the Vema Channel and is bathed by
the NADW core.
North ofthe Vema Channel area, particle concentrations in water depths of the NADW level
show minimum values (Jones 1984), which are also
mirrored by lowest Al\err -values in sediments at the
same water depth (Masse et al. 1996). After
bypassing the Vema Channel region, the jets of
NADW enriched in kaolinite branch offto the central and eastern parts ofthe southermost South Atlantic and partly flow southward into the Argentine
Basin. Thus, NADW that passes the Vema Channel region probably contributes to kaolinite export
fluxes to the ACC.
The modern distribution of chlorite in surface
sediments also shows marked affinities to the recent abyssal circulation (Biscaye 1965; Jones 1984;
Petschick et al. 1996). Maximum concentrations
(20-30 %) occur in the ACC region and the western South Atlantic, reflecting the asymmetric northward extension of southern-source deep and bottom water in the South Atlantic (Petschick et al.
1996).
Potential chlorite sources are the southern polar and subpolar regions, where almost absent
chemical weathering prevents alteration of the nonresistant Fe-bearing clay mineral chlorite. The relationship between source rock geology and maximal chlorite abundances in coastal marine
sediments, suggests that most chlorite in deep-sea
sediments of the South Atlantic and ACC region is
derived from the magmatic arcs and accretionary
rocks of the Patagonian Andes and the Antarctic
Peninsula (Petschick et al. 1996). Both regions are
mainly built up of intrusive calc-alkaline rocks and
sedimentary rocks that have undergone weak lowgrade metamorphism (Miller 1982; Flitterer 1986;
Smellie et al. 1996) and hence are potential chlorite
sources. Most chlorite in marine sediments ofthe
Chilean Archipelago is derived from these rocks
(Siegel et al. 1981). In the vicinity ofthe Antarctic
Peninsula chlorite may also originate from both
Mesozoic and alterated Cenozoic volcanic rocks
(Yoon et ai. 1992) and upper Jurassic sedimentary
rocks from the eastern Antarctic Peninsula, which
contain high amounts of diagenetic chlorite (Bausch
1995).
The preceding considerations suggest that
kaolinite and chlorite in marine deposits of the South
Atlantic and the adjoining Southern Ocean, in contrast to other clay minerals, represent terrigenous
single-source clay minerals from low-latitude and
high-latitude regions with different weathering regimes, respectively. Both clay minerals are exported
via deep water advection in opposite directions
from their sources to distant ocean basins where
they cannot be immediately derived from the surrounding land masses. Both clay minerals are therefore regarded as appropriate tracers of the opposite meridional advection of deep water masses
from northern and southern sources.
The oceanographic significance of kaolinite and
chlorite is well documented by their relative abundances and particularly by the kaolinite/chloriteratio in surface sediments (Petschick et al. 1996).
The comparison oftwo components by their ratios
instead oftheir proportions within a set of components eliminates dilution effects caused by other
components. The kaolinite/chlorite-ratio in surface
sediments shows a zonal decrease from the equator to the ACC region according to the distribution
of kaolinite-bearing NADW in relation to chloritebearing deep and bottom water masses from southern sources (Fig. 2). Even vertical differences of
the kaolinite/chlorite-ratio fit well to the depth-
Diekmann et al.
1996). Apart from local kaolinite-bearing rocks and
soils, no significant continental kaolinite sources
occur between 30 0 S and the Southern Ocean.
Therefore substantial kaolinite transport to the south
can only be achieved through advection of kaolinite
within deep water masses from the north moving
south.
Main jets ofNADW flow are confined to the
continental margins of the western South Atlantic
basins where they constitute the deep western
boundary current above 4000 m water depth
(Faugeres et al. 1993) (Fig. I). On its course to
the south, NADW sweeps off the kaolinite-rich
sediments in the Vema Channel region (Jones 1984;
Masse et al. 1996). Particularly those sediments
trapped at the Sao Paulo Plateau may be entrained
in particulate suspensions of the NADW by reworking and resuspension due to bottom current
turbulence and/or bioturbation (Jones 1984). The
Sao Paulo Plateau forms a broad slope area in 2700
to 3300 m water depth, which builds up the western flank of the Vema Channel and is bathed by
the NADW core.
North ofthe Vema Channel area, particle concentrations in water depths of the NADW level
show minimum values (Jones 1984), which are also
mirrored by lowest Al\err -values in sediments at the
same water depth (Masse et al. 1996). After
bypassing the Vema Channel region, the jets of
NADW enriched in kaolinite branch offto the central and eastern parts ofthe southermost South Atlantic and partly flow southward into the Argentine
Basin. Thus, NADW that passes the Vema Channel region probably contributes to kaolinite export
fluxes to the ACC.
The modern distribution of chlorite in surface
sediments also shows marked affinities to the recent abyssal circulation (Biscaye 1965; Jones 1984;
Petschick et al. 1996). Maximum concentrations
(20-30 %) occur in the ACC region and the western South Atlantic, reflecting the asymmetric northward extension of southern-source deep and bottom water in the South Atlantic (Petschick et al.
1996).
Potential chlorite sources are the southern polar and subpolar regions, where almost absent
chemical weathering prevents alteration of the nonresistant Fe-bearing clay mineral chlorite. The relationship between source rock geology and maximal chlorite abundances in coastal marine
sediments, suggests that most chlorite in deep-sea
sediments of the South Atlantic and ACC region is
derived from the magmatic arcs and accretionary
rocks of the Patagonian Andes and the Antarctic
Peninsula (Petschick et al. 1996). Both regions are
mainly built up of intrusive calc-alkaline rocks and
sedimentary rocks that have undergone weak lowgrade metamorphism (Miller 1982; Flitterer 1986;
Smellie et al. 1996) and hence are potential chlorite
sources. Most chlorite in marine sediments ofthe
Chilean Archipelago is derived from these rocks
(Siegel et al. 1981). In the vicinity ofthe Antarctic
Peninsula chlorite may also originate from both
Mesozoic and alterated Cenozoic volcanic rocks
(Yoon et ai. 1992) and upper Jurassic sedimentary
rocks from the eastern Antarctic Peninsula, which
contain high amounts of diagenetic chlorite (Bausch
1995).
The preceding considerations suggest that
kaolinite and chlorite in marine deposits of the South
Atlantic and the adjoining Southern Ocean, in contrast to other clay minerals, represent terrigenous
single-source clay minerals from low-latitude and
high-latitude regions with different weathering regimes, respectively. Both clay minerals are exported
via deep water advection in opposite directions
from their sources to distant ocean basins where
they cannot be immediately derived from the surrounding land masses. Both clay minerals are therefore regarded as appropriate tracers of the opposite meridional advection of deep water masses
from northern and southern sources.
The oceanographic significance of kaolinite and
chlorite is well documented by their relative abundances and particularly by the kaolinite/chloriteratio in surface sediments (Petschick et al. 1996).
The comparison oftwo components by their ratios
instead oftheir proportions within a set of components eliminates dilution effects caused by other
components. The kaolinite/chlorite-ratio in surface
sediments shows a zonal decrease from the equator to the ACC region according to the distribution
of kaolinite-bearing NADW in relation to chloritebearing deep and bottom water masses from southern sources (Fig. 2). Even vertical differences of
the kaolinite/chlorite-ratio fit well to the depth-